Younger brother is naive. is it normal?

Your brother is not just being naïve; he's behaving like a delusional idiot.

As far as the cost of accommodation is concerned, he could have a look at the following site for real-world prices of something you and he would consider a real flat: https://www.apartments.com/los-angeles-ca/

And he can have a look at the following for details of the glorified closets that might be within his budget: https://www.forrent.com/find/CA/metro-Los+Angeles/Los+Angeles/price-Less+than+1000

I imagine he probably would be able to rent a reasonably sized place for less than $1,000 per month, but I also imagine that would either be in some boondock desert town miles and miles from LA city limits, or in a part of town where the house was regularly ventilated by drive-by shootings.

In any case, his whole "plan" sounds crazy. You say he hasn't got a job lined up. Has he even applied for any teaching jobs? Does he know what qualifications teachers in California must have? Has he looked into whether he'll even be able to get a teaching job without a Green Card? Does he even know what a Green Card is?

What's he planning to do about transportation? All American cities are built with the assumption that everyone has a car and can drive, and LA is particularly bad in this respect. Has he budgeted for buying a car and getting insurance? Does he have a French driving licence? If so, has he looked into what he'll need to do to get an International Driving Permit in English? What's he going to do when the three month limit for using that is up?

And what the hell is this about him acquiring additional dogs to take with him? Has he looked into the cost of air transport of pets from Europe to the USA? (Hint: it isn't cheap!) Has he investigated the rules that apply to live-animal imports into the USA?

Oh, and if he thinks he'll just fly under the radar on the Green Card thing, get into the USA as a tourist and then find work, I can guarantee that the uniformed asshole who checks his passport and asks him the purpose of his visit isn't going to believe he's merely a tourist if he shows up with several dogs in tow.

Seriously, I think you should be considering if he might be going through some sort of mental health crisis. Lots of people his age are naïve, don't really understand how the world works and get carried away by their dreams, but what he's proposing to do is just bonkers.

Is it possible he's bipolar and in a manic phase?

Sounds really stupid. He can move find to a city with cheap rent. Teachers do not make that much either.

My sister used to talk that way about moving to Los Angeles, and becoming a star, until she went to look at an apartment one weekend, then almost miraculously she just shut her pie hole.

I'm curious on how he is entering the USA. You just cannot chose to move to the USA and get a normal job because you decide to.

His ability to get any job legally involves going through the immigration process or having an employer sponsored short term work visa.

If he has a short term work visa he is expected to return to his home country before the visa expires, with the only exception is if he marries in the USA and is accepted though the immigration process; and I've personally met people who married someone from out of the USA and then that person did not make it thought the immigration process and was deported (or refused entry if they married in a foreign country).

He cannot work on a tourist visa.

If you are going to be his sponsor as a family member through the immigration process; you will have to sign to be financially responsible for him for 10 years, unless he gets citizenship himself before then. Consider that carefully...

If he is immigrating based on acceptance based on normal immigration quota's or the immigration lottery; he is in for a huge lesson (and everything except the immigration lottery and refuges status requires evidence of the ability to financially take care of themselves as a condition of approval).

If he's not coming with the appropriate short term work visa or through the immigration process... Then he's likely to find himself kicked out of the USA and not allowed to return - under any visa - for 10 years or more; and if you may find yourself in legal trouble if its found that you assisted him (and deported unless you have citizenship).

Regardless... You cannot stop people who have not learned certain lessons in life from learning them in person.

I wish you well with this,

He'll soon snap out of his naiveness soon. It won't be long.

It would work out well if he moved to the US for a well paying job. Teachers aren't paid well here. At all. You make less teaching in the United States than you do in France.

Yup, that sounds bad.